休眠getResultList（）返回不同的数据

Question

I am working with JPA (1.0 or 2.) + hibernate (3.4.0 or 3.6.0) and I have run into a problem with I think caching somewhere. What I do:

1. Find an object with my JPA class (row in the database with a particular id)
2. update a boolean flag on the object (tinyint field in the database)
3. persist the object
4. grab the entire table from the database with getResultList() hoping to have the change reflected.

Problem:

The change is reflected with getResultList the first time I call it, but the second time it show the previous state. The third time it shows correctly; the fourth, the previous state; etc. It seems to alternate between the two state each time I call getResultList on the table.

Some code for #3 above:

EntityTransaction entityTransaction = entityManager.getTransaction();
entityTransaction.begin();
entityManager.persist(object);
entityTransaction.commit();
entityManager.refresh(object);

Code for #4:

Query query = entityManager.createQuery("from " + object.getName());
List<T> resultList = query.getResultList();

In my efforts to solve the problem, I have:

1.Turned L2 and query cache off in the persistence.xml with:

<property name="hibernate.cache.use_query_cache" value="false"/>
<property name="hibernate.cache.use_second_level_cache" value="false"/>

2.forced a cache eviction before running getResultList() with (using JPA 2.0):

entityManager.getEntityManagerFactory().getCache().evictAll()

3.tried calling refresh() all over the place - to no effect.

Am I missing something?

Any help would be appreciated.

Thanks, sop

Answer 1

I have encountered this issue before (or something very similar) with a few different JPA providers. Make sure that you are explicitly closing your EntityManagers.

Answer 2

I don't think entityManager.refresh(object); is necessary. The default flush mode is Auto, so EntityManager will flush (synchronize the persistence context to the underlying database) at query execution.

Furthermore, does each query entail a SQL query from the database?

Answer 3

Well, Steven, actually your solution did finally end up helping. In my application, I call my updating methods from a Servlet. The problem went away as soon as I closed the EntityManager before I called any of my methods. I still don't know why this works.

Upon closer inspection of the problem, I found that it wasn't getResultList() that was the problem, but when I did a find() on the object in question after updating it, that find() would alternate between two objects with different hashes but same IDs (the different hash was a result of the boolean flag being set or not.)

This is still really weird, but Steven's suggestion worked once I found the right place to do it.